166 Pre-Weaned Calves Have Increased Cortisol Concentrations Post-Wildfire Smoke Exposure

Abstract

Abstract The western states of the U.S., home to some of the largest cattle operations in the country, are increasingly experiencing losses related to wildfire events. Wildfires are predicted to intensify with climate change; rising temperatures, droughts, and drier climatic conditions. Although wildfires do not directly endanger most humans and animals, the resultant smoke can disperse great distances and increase disease susceptibility and death in populations removed from its origin. There is a lack of literature on how wildfire smoke exposure can affect livestock physiology, health, and productivity. Therefore, this study aimed to evaluate changes in blood markers of cattle naturally exposed to wildfire smoke. Eighteen beef-on-dairy calves (Jersey X Simmental) from a commercial farm were enrolled in this study at birth (May to June 2022). Blood samples for analysis of cortisol, acute phase proteins, and pro- and anti-inflammatory cytokines were collected before (June to August), during (September), and after smoke exposure (September and October), in a total of seven collections. Additionally, rectal temperature and health scores were collected from each calf at those time points. Air quality (AQ) data, specifically particulate matter (PM2.5; EPA standard for AQ; 35 µg/m3) near the study location (Vale, OR), was obtained from the AirNow database. For statistical analysis, calf was considered the experimental unit, and all data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Air quality before smoke exposure was considered adequate, and PM 2.5 was, on average, 4.9 µg/m3 from June to August. In September, a wildfire reduced AQ at the study location, increasing PM 2.5 to an average of 44.6 µg/m3 for four consecutive days. After the fire was contained, AQ improved, and PM2.5 dropped to 8.6 ug/m3. Blood cortisol concentrations changed over time (P < 0.001). Cortisol concentrations of samples collected before smoke exposure did not differ (P = 0.89) at 4.4, 2.0, and 1.9 ng/mL (SEM:1.3). Cortisol concentrations increased (P < 0.001) and peaked during smoke exposure, at 10.3 and 7.0 ng/mL (SEM:1.4). Immediately after smoke exposure, cortisol concentrations averaged 6.3 ng/mL, intermediate between those before and during smoke exposure (P = 0.89; SEM:1.3). Interestingly, in the last post-smoke exposure sample, cortisol concentration averaged 9.5 ng/mL, similar to concentrations during smoke exposure (P = 0.99; SEM:1.3). This increase in cortisol concentration post-smoke exposure was unexpected but likely explained by the calves having been weaned two days before this final sampling. In summary, calves naturally exposed to wildfire smoke had increased blood cortisol concentrations with concentrations similar to those observed shortly after post-weaning, a practice known to be challenging and stressful for calves.